1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, which are suitable particularly for a broadcasting television camera, a motion picture camera, a video camera, a digital still camera, a silver halide film camera and the like.
2. Description of the Related Art
In recent years, a large format camera which has such features that a depth of field is small and a blurring taste is beautiful so as to widen video expression is used for an image pickup apparatus such as a television camera, a motion picture camera, a video camera and a photographic camera. A zoom lens which is mounted on the large format camera has been desired to have a high zoom ratio and a high optical performance so as to enhance a latitude of photography. As for the zoom lens having the high zoom ratio, a positive-lead type zoom lens is known which has a lens unit having a positive refractive power arranged in the closest side to an object and includes four or more lens units as a whole, as is proposed in Japanese Patent Application Laid-Open No. 2011-175185 and Japanese Patent Application Laid-Open No. 2012-150248.
Generally, as the image size of the image pickup apparatus is larger, the off-axial aberration of the zoom lens to be mounted thereon becomes large accordingly. Therefore, when the zoom lens is mounted on an image pickup apparatus having a large image size, the optical performance of the zoom lens becomes a problem particularly in the perimeter of an image area.
The above described positive-lead type zoom lens comparatively easily attains a high zoom ratio. However, to further achieve the high zoom ratio in the zoom lens particularly for the large format camera, a zoom variation of the off-axial aberration such as the lateral chromatic aberration increases, and it is difficult to achieve both of the high zoom ratio and the high performance.
In order to achieve the high zoom ratio and the high performance in the above described positive-lead type zoom lens, it is important to appropriately set a refractive power particularly of a lens unit in a closer side to the image than an aperture stop, on which an incidence height of an off-axial principal ray is high.